This invention relates to metal casting apparatus and methods which employ gas permeable shell molds.
Gas permeable shell mold casting for casting of metal in an evacuated/inert gas atmosphere is known and is disclosed in U.S. Pat. Nos. 3,863,706; 3,900,064; 4,112,997; and 4,340,108. Gas permeable shell mold casting was developed to permit precision casting, on a high production basis, of metals which must be cast in an evacuated or inert gas atmosphere. Prior to the development of gas permeable shell mold casting, precision casting of metals in an evacuated or inert gas atmosphere presented a number of problems. In part, those problems were due to the time necessary to establish the required seals and to evacuate the casting apparatus, especially insofar as the relatively large melting and pouring chamber was concerned. There were also problems caused by the inclusion in the cast parts of dross or other impurities present on the surface of the molten metal.
Although gas permeable shell mold casting solved many of the problems of casting metals in an evacuated or inert gas atmosphere, problems still remain. The most critical problem is in providing a constant level of molten metal to the mold. Until the present invention, this problem has remained largely unsolved.
It is therefore an object of the invention to provide an apparatus and method for providing a constant level of molten metal to a mold in gas permeable shell mold casting which is simple, effective and reliable. Other objectives and advantages of the invention will become apparent hereinbelow.